Combined effect of structural softening and magneto-elastic coupling on elastic coefficients of Ni Mn Ga austenite

Magnetic Domain Walls and Macroscopic Magnetization-Related Elastic and Anelastic Effects during Premartensitic Transition in Ni2MnGa

“…Figure 2a,b shows the IF and YM versus temperature for the demagnetized state of the sample and under moderate (below saturation) fields. Since E100≈3C′ in cubic Ni 2 MnGa, the values of the effective YM in the demagnetized state are in good agreement with previous data on C′, as obtained by RUS over the same temperature and frequency ranges [6,13,38]. A double IF maximum and corresponding double YM minimum are observed over the PMT range for the demagnetized state.…”

Elasticity and magnetism of Ni2 MnGa premartensitic tweed

“…The and constants were measured by a conventional pulse‐echo method, i.e., from times‐of‐flight of ultrasonic longitudinal and shear waves, respectively, between the largest faces of the sample. As the pulse‐echo method is less suitable for the determination of the coefficient particularly for material with large elastic anisotropy, this shear modulus was measured by resonant ultrasound spectroscopy (RUS), see for more details on these measurements. To determine the effect of the magnetic field, the soft (i.e., in demagnetized state) and hard elastic modulus (i.e., in magnetic saturation ()) were measured at zero field and at field of 0.4 T, which is above magnetic saturation of the sample ().…”

“…However, the magnetic properties of austenite and premartensite are quite similar and hard to distinguish. On the other hand the detailed investigation of the evolution of elastic constants in magnetic field and temperature in austenite and premartensite reveals that elastic coefficient , instrumental for premartensite transformation, is strongly dependent on magnetic field particularly in austenite phase . The scales with square of magnetization revealing strong magnetoelastic coupling.…”

Softening of Shear Elastic Coefficients in Shape Memory Alloys Near the Martensitic Transition: A Study by Laser-Based Resonant Ultrasound Spectroscopy

“…For the austenite phase, a pronounced change of the dc /dT slope occurs at the Curie point. As discussed in [40,41], this change is caused by the magneto-elastic coupling, which effectively softens the austenite lattice. In other words, below T C the softening of the austenite phase can be decomposed into two parts: the first is ascribed to the TA 2 phonon-induced softening and retains approximately the same dc /dT slope as above the Curie point (the dash-dot line in Figure 3a), and the second to the magneto-elastic coupling.…”